SDMX Category Structure Module The category structure module defines the structure of category scheme and category constructs. CategorySchemeType describes the structure of a category scheme. A category scheme is the descriptive information for an arrangement or division of categories into groups based on characteristics, which the objects have in common. This provides for a simple, leveled hierarchy or categories. The id attribute holds the identification of the category scheme. The type of this id is restricted to the common:NCNNameIDType. This is necessary, since the category scheme may be used to create simple types in data and metadata structure specific schemas and therefore must be compliant with the NCName type in XML Schema (see common:NCNameIDType for further details). Category represents a set of nested categories which describe a simple classification hierarchy. CategoryType describes the details of a category. A category is defined as an item at any level in a classification. The Category element represents a set of nested categories which are child categories.